2004 Ford Taurus My car fuses go crazy.

I have a 2004 ford taurus. Unfortunately I couldn't start it because the battery died. I checked both alternator and battery and they both good, but the car still doesn't start. The fuses just turn on and off like crazy underneath the dashboard and after a few seconds the dashboard display turns on and functions normally. But when I do that like two or three times, the display looks as if it has no battery when actually it has a new one. What could be wrong? Also when the engine belt was taken off it fitted perfectly, now when we try to put it back on, the belt fits too big.(It is exactly as in the car manual's diagram) what could be wrong?